The present invention relates to hydraulic oil and to a method for manufacturing hydraulic oil.
Hydraulic oil refers to a fluid which is intended to transmit power or carry a load in various systems. Hydraulic oil is used in different stationary and mobile machines, such as cylinders performing a linear movement or rotating hydraulic motors.
In addition to power transmission, the function of hydraulic oil is to lubricate mobile parts in the components of the system and to cool the system.
Hydraulic oil has to fulfill the following requirements:
1. Suitable viscosity at different temperatures
2. Sufficient pressure endurance
3. Non-foaming properties
4. Oxidation inhibition
5. Corrosion inhibition
6. Inert quality
In addition to these qualities, biodegradability has become more important in the past few years, particularly in hydraulic oils to be used in work machines moving outdoors.
Finnish Patent No. 95367 presents a method for manufacturing a synthetic ester from vegetable oil. This publication describes manufacturing of trimethylolpropane ester of rapeseed oil by transesterification starting from a mixture of lower alkyl esters of the fatty acids of rapeseed oil, obtained by transesterification of vegetable oil with lower alkanols. Finish Patent No. 95367 also describes manufacturing of methyl ester of tall oil, but this does not take place by transesterification reaction, and there is no description on the further processing or use of the methyl ester.
The object of the invention is to present a hydraulic oil whose raw material is amply available as an industrial by-product and which is biodegradable. The object of the invention is also to present a method for manufacturing such a hydraulic oil in a simple manner which does not require many reaction stages. The basic material of the hydraulic oil is a tall oil ester which is selected from the following substances or their mixtures:
ester of a polyhydroxy compound of neopentane, such as
trimethylolpropane ester (TMP ester),
pentaerythritol ester,
trimethylolethane ester,
trimethylolbutane ester,
neopentyl glycol ester, and
poly(ethyleneglycol) ester.
It has been found that esterification of a di- or polyvalent alcohol containing at least five carbon atoms with tall oil gives a hydraulic oil having a viscosity in the suitable range and, after addition of certain additives, having also surprisingly good properties for a hydraulic oil. Further, the viscosity properties of the oil can be controlled by adding small amounts of some lower ester of tall oil, particularly its ethylene glycol ester. Lower esters refer to esters obtained with an alcohol being bivalent (dihydroxy) at most and having fewer carbon atoms than the polyols listed above, or being monovalent, wherein it can have more carbons in its carbon chain. This ester has by nature a lower viscosity than the above-listed polyol esters.